1. Field of the Invention
The present invention relates to a mobile broadcast system, and more particularly to a method of processing a short-term key message in a terminal supporting mobile broadcast, and a terminal therefor.
2. Description of the Related Art
The Open Mobile Alliance (OMA) group researches standards for interworking among individual mobile solutions, and specifies two profiles as a broadcast standard established to be used appropriately for broadcast environment. One of the profiles is a Digital Rights Management (DRM) profile, and the other is a smart card profile. In the smart card profile, a video/audio stream encrypted with specific keys is transmitted to a terminal over a broadcast network. Further, a data stream having keys necessary for decrypting the encrypted video/audio stream is also transmitted to the mobile terminal over the same broadcast network, which is referred to as a Short-Term Key Message (STKM).
In the smart card profile, the received STKM is subjected to a resending check by a Multimedia Internet KEYing (MIKEY) parser in the mobile terminal. Here, a Multimedia Broadcast/Multicast Service (MBMS) Traffic Key (MTK) included in the STKM is changed once every several seconds or minutes, and the STKM is transmitted every 0.5 seconds or every several seconds, thereby causing the mobile terminal to receive the same STKM several times or several tens of times until the key is updated once. Continuously performing a parsing and a key decryption every time the STKM is received results in a waste of mobile terminal resources. Therefore, as a method of reducing this resource waste, a resending check is essential.
For the resending check, the STKM to be transmitted in a MIKEY message structure is used in the smart card profile. The MIKEY message structure is described as shown in FIG. 1 and the MTK is formatted by a simple binary encoding method, such as the MIKEY, in order to be transmitted. In particular, as a decision reference for the resending check, an MTK IDentification (ID) included in an MBMS EXT (Extension) 100 field in FIG. 1 is used.
A procedure of the resending check will now be described with reference to FIG. 2. FIG. 2 shows an operational flowchart of a mobile terminal for a conventional resending check.
Referring to FIG. 2, the mobile terminal determines whether an STKM is received, in step 200. If the STKM is received, the mobile terminal performs the resending check in step 205, and determines whether the received STKM is a new STKM in step 210. If the received STKM is not a new STKM, the mobile terminal goes to step 215 and discards the received STKM. If the received STKM is a new message, a parsing and key decryption process is performed on the mobile terminal or the smart card according to a location of a secure function. The process is classified into a Generic Bootstrapping Architecture (GBA)-Mobile Equipment (ME) (GBA_ME) scheme or a GBA_Universal Subscriber Identity Module (USIM) (GBA_U) scheme according to whether a location for processing the STKM in the smart card profile is a mobile terminal or a USIM, i.e., a smart card. In the GBA_U scheme, the STKM is delivered to a USIM by an Application Protocol Data Unit (APDU) command, and then the parsing and key decryption process is performed within the USIM. Then, the MTK or a Traffic Encryption Key (TEK) included in the STKM is delivered again to the mobile terminal.
At this time, when a separate MIKEY parser is included in the mobile terminal for analyzing the STKM, the mobile terminal analyzes the MIKEY and stores the result information according to the analysis by performing the parsing operation, in step 220. Thereafter, the mobile terminal determines whether a response message is received from the USIM, in step 225. When the response message is received, the mobile terminal obtains the TEK by parsing the response message, in step 230. Subsequently, the mobile terminal delivers the stored result information and the TEK to a player, in step 235.
In the player, a variety of information is required for reproducing a video/audio stream. However, in the case of the GBA_U scheme, a variety of information is included in the STKM, but the USIM delivers the only TEK. Therefore, since the mobile terminal must perform the parsing operation by using the separate MIKEY parser and have the values in a memory, the parsing operation causes memory and resources in the mobile terminal to be wasted. Moreover, independently from the parsing and key decryption procedure within the USIM, redundant operations are unnecessarily performed in the mobile terminal by analyzing the MIKEY and by analyzing the result information, which increases the load on the mobile terminal.